The invention relates to a method for the drying of moisture-containing powder-like products, particularly starches and flours, using a drying device of the type mentioned in the preamble of patent claim 1, respectively an apparatus for carrying out this method.
Such a drying device is described in more detail in German patent No. 1,066,955. It is highly economical because the drying product is passed pneumatically in a helical path under contact with the heated inner drying wall through the drying device, whereby despite short dwell times over the entire dryer length of the path a high heat transmission to the drying product is obtained. Accordingly, the drying device known as a rotary tube dryer in practice has become widely accepted and suitable for many applications. Difficulties in use exist, however, in the case of those powder-like products which tend to stick when in moisture-laden condition, whereby the flow relationships in the dryer are substantially interrupted over the entire cross-section of the same.
In the treatment of extremely moisture-laden starch products, such as, e.g., corn starch or potato starch in the dryer, particularly the inlet region thereof clogs by the caking of these products at the inner wall of the dryer. Heretofore it was necessary to demoisturize such products in a convection dryer being supplied with large quantities of carrier gas, whereby the occurrence of clump-formation and product caking at the dryer wall was avoided.
Due to the high carrier gas quantities, however, these dryers are not only structurally expensive but also consume huge amounts of energy.